Benz isothiazole 1,1-dioxide

Thiosaccharin is reduced by the borane-dimethyl sulfide complex to 2,3-dihydro-1,2-benz-isothiazole 1,1-dioxide <90JCR(S)106>. Sodium borohydride reduces 3-substituted 1,2-benzisothiazole... 

Another application of the well-known cyclization of ortV o-substituted benzenesulfonamides consists in the treatment of 415 (R =NR2, R = Me) with Et30Bp4 followed by aqueous H2SO4 affording good yields of benz-isothiazol-3-one 1,1-dioxides 416. Their alkaline hydrolysis afforded 415 (R = OH, R = R = H), which is stable at neutral pH but recyclizes to 416 under even mild acidic conditions (pH <4) <1999T237>. 

From the results of 4H NMR studies14 and X-ray analysis of 712 the conclusion was drawn that the ground state of substituted 3-amino-benz[d]isothiazole-1,1-dioxides is best represented by structures (7a) and (9a). 

The mass spectrometric fragmentation of selected compounds representing most of what is covered in this review has been analyzed recently.20 Apart from typical fragmentations (loss of SO 2 rearrangement followed by loss of CO, etc.) the pattern is frequently dominated by the fragmentation of substituents. The MacLafferty rearrangement of 3-substituted benz[d]isothiazole-1,1 -dioxides with a proton in the appropriate position resembles the thermal fragmentation28 (cf. Section XII). 

N-Acyl saccharins (13) in part resemble iV-alkyl saccharins in their reactions. From the hydrolysis of 3-oxo-2-acetyl-6-chloro-2,3-dihydro-benz[d]isothiazole-1,1-dioxide (64) with a base/alcohol mixture one obtains iV-acetyl-4-chloro-2-sulfamoylbenzoic acid (65). On heating with base the acetyl group is hydrolyzed off.180... 

The critical temperature for the thermal rearrangement of 3a under various conditions (in the melt,96 in quinoline20 or naphthalene17) appears to be in the vicinity of 180°. The 3-methoxy derivative (70) isomerizes readily with lithium iodide (in methyl ethyl ketone at 64°).17,96 When ethyl iodide is added to this reaction, i r-methylsaccharin (8) and iV-ethylsaccharin (22) are formed together.96 Lithium iodide catalysis is particularly useful in rearranging nucleoside derivatives, e.g., 71.17 The 3-benzyloxy derivative (73) reacts with debenzylation.17 Even more complex systems like derivatives of steroid alcohols17,20 are isomerized on heating in reasonable yields. When the optically active 3-(2-(cZ)octyloxy)benz[d]isothiazole-l, 1-dioxide was thermally re-... 

Alkaline hydrolysis of 5a appears to pass through l,244 leading to the same final product (o-carboxybenzenesulfonamide). The monomethyl and ethyl derivatives (9 R = Me, Et) hydrolyze slowly to 1 in dilute alkali,13 3-(o-carboxyanilino)benz[d]isothiazole-l, 1-dioxide (77) and functional derivatives form a tetracyclic system (78) on treatment with... 

The acetophenonoxime pseudosaccharin ether affords 3-anilino-benz[d]isothiazole-1,1 -dioxide (80) and apparently ketene under comparable conditions.254, 259 A similar mechanism involving 95 may be operative in the formation of 5b from 19 and dialkylcarbamoyl... 

XII. Elimination Reactions with 3-Substituted Benz/d/isothiazole-1,1-dioxides... 

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